The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines draw air into an intake manifold through an inlet system that may be regulated by a throttle. The air in the intake manifold may be distributed to a plurality of cylinders and combined with fuel to create an air/fuel (A/F) mixture. The fuel may be provided via a plurality of fuel injectors located at intake ports of the cylinders (i.e., port fuel injection) or in the cylinders (i.e., direct fuel injection). The A/F mixture may be compressed by pistons and combusted within the cylinders to drive the pistons and rotatably turn a crankshaft generating drive torque. The drive torque may be transferred from the crankshaft to a driveline (e.g., wheels) of a vehicle via a transmission.
Homogeneous charge compression ignition (HCCI) engines may operate in one of a plurality of modes depending on operation conditions. Specifically, HCCI engines may operate in a spark ignition (SI) combustion mode, an HCCI combustion mode, or a mixed combustion mode. For example, the HCCI combustion mode may be used at medium engine loads and the SI combustion mode may be used at high engine loads. The mixed combustion mode, on the other hand, may be used during low engine loads.
Specifically, the SI combustion mode may include compressing the A/F mixture and igniting the compressed A/F mixture with spark provided via spark plugs in the cylinders. The HCCI combustion mode, on the other hand, may include compressing the A/F mixture until a critical pressure and/or temperature is reached and the A/F mixture automatically combusts. In the mixed combustion mode, multiple ignition and fuel injection events may occur to promote HCCI combustion. In other words, the mixed combustion mode may include compressing the A/F mixture until the A/F mixture automatically combusts, meanwhile providing “assistance” to the combustion with pre-injection of fuel and pilot ignition provided via the spark plugs (“spark assist”).